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RequiredFieldValidator.EvaluateIsValid Method

Called during the validation stage when ASP.NET processes a Web Form.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

protected override bool EvaluateIsValid()

Return Value

Type: System.Boolean
true if the value in the input control is valid; otherwise, false.

The following code example demonstrates how to override the EvaluateIsValid method in a custom server control so that it always returns false if the value of the RequiredFieldValidator is null or empty, and always returns true otherwise.


<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.CS.Controls" Assembly="Samples.AspNet.CS" %>
<%@ Page Language="C#" AutoEventWireup="True" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>Custom RequiredFieldValidator - EvaluateIsValid - C# Example</title>
    <script runat="server">
      void Button1_Click(Object sender, EventArgs e) 
      {
        if (Page.IsValid) 
        {
          Label1.Text = "Required field is filled!";
        }
        else 
        {
          Label1.Text = "Required field is empty!";
        }
      }
    </script>
  </head>
  <body>
    <form id="Form1" method="post" runat="server">
      <h3>Custom RequiredFieldValidator - EvaluateIsValid - C# Example</h3>

      <table border="0" cellpadding="4" cellspacing="0">
        <tr valign="top">
          <td colspan="3">
            <asp:Label ID="Label1" runat="server" Text="Fill in the required field below" />
          </td>
        </tr>
        <tr>
          <td align="right">Card Number:</td>
          <td>
            <asp:TextBox id="TextBox1" runat="server" />
          </td>
          <td>
            <aspSample:CustomRequiredFieldValidatorEvaluateIsValid 
              id="RequiredFieldValidator1" 
              runat="server" 
              ControlToValidate="TextBox1" 
              Display="Static" 
              ErrorMessage="*" />
          </td>
        </tr>
        <tr>
          <td>&nbsp;</td>
          <td>
            <asp:Button 
              id="Button1" 
              runat="server" 
              Text="Validate" 
              OnClick="Button1_Click" />
          </td>
          <td>&nbsp;</td>
        </tr>
      </table>

    </form>
  </body>
</html>


...


using System.Web;
using System.Security.Permissions;

namespace Samples.AspNet.CS.Controls
{
  [AspNetHostingPermission(SecurityAction.Demand, Level=AspNetHostingPermissionLevel.Minimal)]
  public sealed class CustomRequiredFieldValidatorEvaluateIsValid : System.Web.UI.WebControls.RequiredFieldValidator
  {
    protected override bool EvaluateIsValid()
    {
      // Get the ControlToValidate's value.
      string controlValue = GetControlValidationValue(ControlToValidate);

      // If ControlToValidate's value is null or empty, then return false.
      if ((controlValue == null) || (controlValue.Trim().Equals(System.String.Empty)))
      {
        return false;
      }
      // Else the control contains a value so return true.
      else
      {
        return true;
      }
    }                
  }
}


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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